Polyethylene compositions



United States P2113 er. No. 52,784

5 Claims. (Cl. Zed-32.6)

This invention relates to plastic compositions and, more specifically,to novel polyethylenes of enhanced slip characteristics.

This application is a divisional of our copending application Serial No.742,755, filed June 18, 1958, now Patent No. 2,991,265.

Polyethylene is one of the most popular and well known thermoplastics ofthis plastic age. The number of varied uses increases spectacularly eachyear; many of these include the utilization of polyethylene films.Polyethylene film is being used to package a wide and varied list ofcommercial commodities such as foods, meats, chemicals, pharmaceuticals,seeds, clothing, hardware and toys. One of the more important propertiesassociated with polyethylene film is its slip or film-to-filrncoefficient of friction. Slip, as it is known to the trade, relates tothe resistance of the film to a sliding action over another filmsurf-ace or over a metal surface, as manifested by the thin sheets ofblown film sticking to one another. Poor slip characteristics ofpolyethylene film are especially troublesome to users of automaticpackaging equipment. Poor slip is a greater problem with blown film,which is usually thinner than extruded sheets, although there are alsomany applications of sheets in which an improved slip is alsoadvantageous.

The object of this invention is to provide plastic compositions havingan improved slip or low film-to-film coetficient of friction. A furtherobject of this invention is to provide polyethylene compositions which,upon con- 7 12 to 18 carbons and particularly the alkyl groups having 12to l8 even numbered carbons. The alkyl is advisably a straight chain.Furthermore, the additive should have a melting point of less than 69 C.Some particular compounds within this group that might be named, andwhich are good polyethylene slip additives, are N-(ndodecyl)oleamide, N(n myristyl)oleamide, N-(n-palmityl)oleamide andN-(n-octadecyllolearnide.

Additives of the described types are solids at room temperature,insoluble in water and soluble in most hot hydrocarbons. These compoundsare readily prepared by conventional processes such as by heating theappropriate 3,108,98l Patented (Pet. 29, 1963 fatty acid with theappropriate amine at about 230 C. for about 0.5 to 1 hour under anatmosphere of nitrogen. The product is recovered from the reactionmixture by theusual procedures.

The incorporation of a small amount of one or more of the describedadditives in polyethylene greatly reduces the polyethylene coefficientof friction. Polyethylene films and sheets and other products made frompolyethylene containing a small amount of an additive possess improvedslip characteristics.

Incorporation of the additive in the polyethylene may be eifected byseveral different methods. For example, the additive may be added as asolid, in solution or in the form of a slurry to polyethylene in eitherthe molding power or pellet form followed by tumbling and drying. Theadditive may also be incorporated by melt blending the ingredients in aconventional apparatus, such as a banbury mixer, heated rolls or aplasticater.

Additives of the described types are effective slip agents whenincorporated in polyethylene to give a polyethylene compositioncontaining about 0.01% to about 1% by weight of the additive. Thepreferred composition is about 0.05% to about 0.2% by weight of additivein polyethylene. Although more than 1% of additive may be incorporatedin polyethylene, larger amounts would not generally be warranted.

It is to be understood that minor amounts of other desirable materials,such as high melting waxes, antioxidants, dyes and pigments, lubricants,antistatic agents, and the like, may also be present in amounts which donot affect the high slip properties of these polyethylene compositions.

The described additives are effective in improving the slipcharacteristics of all types of polyethylene, whether they be the morelinear polyethylenes prepared by the low pressure process," theconventional high pressure process polyethylenes of a lower density orthe medium ensity polyethylenes.

Although polyethylene containing one or more of the described additivesis particularly useful for improving the slip of products fabricated byextrusion into thin films, sheets, blown tubing, and the like, it mayalso be cast or molded into films, sheets, rods, tubes and piping,filamerits, and other shaped articles, having better slip than similarproducts made of polyethylene containing no additive. In this regard,molded articles such as cups which tend to stick together when nestedare more readily separated when the polyethylene contains at least oneof the described additives. The polyethylene compositions of thisinvention may also be used for coating paper, cloth, wire, metal foil,glass fiber mats and synthetic and natural textiles where good slip isdesired.

Polyethylene to which at least one of the additives is added hasimproved blocking properties, that is, film made from such polyethylenehas much less tendency to block than an identical polyethylenecontaining no additive.

The following example illustnates the improved effect of the additiveson the slip of polyethylene sheet.

Example 1 Various additives of the described group were introduceusingly into a commercial high pressure process type polyethylene havinga density of 0.92 and melt index 3 of 2 by introducing the additivesinto a commercial type banbury :and banburying for 10 minutes at 190 F.The polyethylene was then sheeted on a roll mill, ground on a Wiley milland screened throng a screen having 4 mm. openings and extruded intoflat film on a 1-inch extruder equipped with a 6-inch fiat film die. Thefilm was aged by suspending in air at room temperature for at least 24hours. The film was evaluated for slip by means of an inclined planemethod, which consisted of stretching the film on an adjustable plane. Ametal sled weighing 95 grams was placed on the film and one end of theplane then raised until the sled began to slide. The slope of the planeat this point, expressed in degrees, was reported as the slip of theadditive.

The following results were 15 from 0.01% to 1.0% by weight ofN-(n-dodecyDoleamide.

2. A plastic composition comprising polyethylene and from 0.01% to 1.0%by weight of N-(n-myristyl)oleamide.

3. A plastic composition comprising polyethylene and from 0.01% to 1.0%by weight of N-(n-palmityl)oleamide.

4. A plastic composition comprising polyethylene and g from 0.01% to1.0% by Weight of -N-(n-octadecyl)o1eobtained: amide.

Table Slip Angle at Cone. of- Additive Formula ll N-(n-dodecyl) oleamideCl7H330-NH-(CH2)i1CH3-- 27 21 15 12 7 ll N-(n-myristyl) oleamideC17H33C-NH-T(CH2)13CH3. 28

, n N-(n-paln1ityl)oleam1de CHHMC-NH-(OHDuC 24 l? N-(n-octadeeyl)oleamide C11HazC--N'H(CHz)17CHs 18 Control (no additive) 36.

The results clearly show the improved slip characteristics of thepolyethylene-additive compositions. The control containing no additiverequired an angle much higher than the polyethylene-additivecompositions in order to cause the sled to slide. We have found thatpolyethylene compositions which have a low film-to-metal coefficient offriction will also have a comparably low film-to-film coeflicient offriction.

5. A plastic composition comprising polyethylene and 0.01% to 1.0% byweight of an N-monoalkyl oleamide, said alkyl group having 12 to 18carbons andsaid N monoalkyl oleamide having a melting point of less thanReferences Cited in the file of this patent FOREIGN PATENTS France Nov.5, 1956

5. A PLASTIC COMPOSITION COMPRISING POLYETHYLENE AND 0.01% TO 1.0% BYWEIGHT OF AN N-MONOALKYL OLEAMIDE, SAID ALKYL GROUP HAVING 12 TO 18CARBONS AND SAID NMONOALKYL OLEAMIDE HAVING A MELTING POINT OF LESS THAN69*C.